Import a set of issues into a new epic

We are using another software to create a WBS and time planning. After we do that, we export all issues into CSV and are importing them into Jira. After we import issues into Jira, they are not associated automatically into the epics we have defined in the CSV. Also, we would like to precreate sprints for epics in the same import task. Which field in Jira is responsible for associating issues to epics and issues to sprints so we can add that info before exporting them and have them already created on the import phase?